Concrete anchor fastening systems for particular use in connection with concrete substrate structures, such as, for example, those systems for securing or fastening roofing insulation materials to concrete decking, are of course well known. One such well known fastening system comprises the STRIKER.TM. concrete anchor fastening system which has been developed and marketed by ITW BUILDEX, 1349 West Bryn Mawr, Itasca, Ill. 60143, a subsidiary of the assignee of record of the present patent application embodying the present invention. The STRIKER.TM. concrete anchor fastening system is disclosed within FIG. 1 and is generally indicated by the reference character 10. The STRIKER.TM. concrete anchor fastening system 10 is adapted to secure or fasten roofing materials, such as, for example, sheets of rigid roofing insulation 12 to a concrete substrate or substructure 14, and is seen to comprise a STRIKER.TM. concrete anchor 16 and a STRIKER.TM. plate 18 operatively associated therewith. The STRIKER.TM. plate 18 may optionally be fabricated as either a metal plate or a plastic plate.
In accordance with the recommended installation techniques to be employed in connection with the aforenoted prior art STRIKER.TM. concrete anchor fastening system 10, a standard or conventional rotary hammer drill is first used to drill a pilot hole through the insulation 12 and into the concrete substructure 14, the pilot hole having an axial depth which is at least one-quarter inch (1/4") deeper than the final engagement depth of the concrete anchor 16 so as to accommodate, for example, debris from the drilling operation. STRIKER.TM. plate 18, along with the STRIKER.TM. concrete anchor 16 which may be pre-assembled therewith by insertion through a central aperture 20 thereof, is then positioned atop the rigid insulation 12 such that the concrete anchor 16 can be inserted into the drilled pilot hole. The STRIKER.TM. concrete anchor 16 can then be fully inserted through the rigid insulation 12 and into the concrete substructure 14 by means of a suitable hammer or other type of impact tool.
As can be seen from further reference to FIG. 1, the STRIKER.TM. concrete anchor 16 is of the type comprising a pointed tip portion 22, a head portion 24, and a body or shank portion 26. The body or shank portion 26 is provided with a circumferentially arranged series of substantially axially extending, alternating ribs and grooves 28, the ribs and grooves 28 preferably having a slight spiral or twisted orientation with respect to the longitudinal axis of the anchor 16. The outer diametrical extent of the ribs is greater than the corresponding diametrical extent of the pilot hole drilled within the rigid insulation 12 and concrete substructure 14 such that when the concrete anchor 16 is hammered into the concrete substrate or decking 14, a good interference fit is defined between the concrete anchor 16 and the annular surrounding wall surfaces of the concrete substructure defining the pilot hole drilled therein. This interference fit defined between the concrete anchor 16 and the surrounding walls of the pilot hole drilled within the concrete decking 14 serves to determine the retaining force or pull-out resistance characteristic of the concrete anchor 16. The retaining force or pull-out resistance characteristic of the concrete anchor 16 should of course be sufficient to prevent the concrete anchor 16 from becoming dislodged from the concrete decking 14 even, for example, s,under high wind conditions, which create large uplift force so as to in fact maintain the rigid insulation 12 affixed to the concrete decking 14.
While the aforenoted prior art STRIKER.TM. concrete anchor fastening system 10 has been extremely commercially successful, it has been realized that in view of the fact that the series of ribs and grooves 28 extend axially throughout substantially the entire axial length of the concrete anchor 16, that is, along substantially the entire axial length of the shank portion 26 defined between the tip portion 22 and the head portion 24, the STRIKER.TM. concrete anchor 16 is of the type which is characterized as depth-sensitive A depth-sensitive fastener exhibits driving characteristics wherein the driving or impact force required to install the anchor 16 within the pilot hole of the concrete decking 14 and rigid insulation 12 is directly proportional to the depth of embedment of the installed fastener, or in other words, the deeper the fastener is driven into the drilled pilot hole, the more difficult it is to install the STRIKER.TM. concrete anchor 16 because of the ever-increasing axial length of the plurality of ribs that encounter the sidewall portions of the concrete decking 14, defining the driller pilot hole and which define the aforenoted interference or friction fit with the ribs of anchor 16, as the anchor 16 is progressively axially inserted into the pilot hole.
In an effort to overcome the aforenoted installation difficulties attendant the prior art STRIKER.TM. anchor 16, depth-insensitive anchors have been developed. One such anchor is disclosed in U.S. Pat. No. 5,035,559 which issued to Martin J. Nilsen on Jul. 30, 1991 and is assigned to the assignee of record of this patent application. This particular type of anchor, however, is substantially different from the STRIKER.TM. anchor 16 in that in lieu of defining an interference or friction fit between the STRIKER.TM. anchor and the sidewalls of the concrete deck defining the drilled pilot hole as in the case of the system disclosed in FIG. 1, the concrete anchor disclosed in U.S. Pat. No. 5,035,559 is of the compression fit type in that the shank of the anchor of such patent undergoes bending and straightening deformations as the shank portions of the anchor, offset with respect to each other and with respect to the longitudinal axis of the anchor, encounter the sidewall portions 52 of the hole 50 defined within the body of concrete 54.
Another anchor for use within concrete or masonry, and of the interterference-fit type, is disclosed in U.S. Pat. No. 4,350,464 which issued to Richard L. Brothers on Sep. 21, 1982. This anchor, however, is not truly of the depth-insensitive type in view of the fact that the diameter of the shaft 13 of the anchor 10 has a diametrical extent which is substantially or essentially the same as that of the hole 101 formed within the concrete 100. In addition, the anchor of this patent is quite difficult and costly to manufacture in view of the need for the anchor shank portion to undergo bead line welding in order to provide the anchor 10 with the patterned weld bead lines 14.
A need therefore exists within the concrete fastener system art for a new and improved depth-insensitive concrete fastener system which employs a depth-insensitive concrete anchor of the interference or friction-fit type.